careful!!!
My iMac was flickering out of the box. the first "graphics firmware update 1.0" that came out Dec 21 cured it. I installed this latest firmware update today (Display Firmware Update 1.0) and now my screen is flickering every few seconds!! And the worst part is, I forgot to time capsule before the update. I recommend everyone avoid this update if your screen isn't already flickering.
good luck,

And just an FYI: A backup will not take you back to before a firmware update. A firmware update updates your hardware. It is not an update that is applied into your OS that can simply be undone by a restore. To undo a firmware update you would need to re-install an earlier firmware.

Unless a particular firmware is advised for all users of a device, it is typically not advised unless you are experiencing the issues which that particular firmware addresses.

I cannot be held responsible for the things that come out of my mouth.
In the Windows world, most everything folks don't understand is called a virus.

Exactly what does this so called flickering look like?
I am only asking because of late when my iMac 27" comes out of sleep mode the odd time it goes right back into sleep mode but does come out once I activate via keyboard,mouse etc..Once I begin working on the computer there is no issue.
Thanks in advance.
Pete.

What you described is not "flickering". The flicker problem is similar to a fast blinking light - on - off very quickly. The Apple discussion forums have dozens of different descriptions you can look over if you like. LINK